Labelling machines are commonly used to apply labels to containers of all sorts. These machines are very often used with bottles or other vessels destined to hold pourable food products are tubular labels (also commonly called “sleeve labels”) which are obtained by:                cutting a web unwound from a supply roll into a plurality of rectangular or square portions;        winding each web portion in a tubular configuration such that opposite vertical edges overlap; and        welding the overlapping edges to fix the web material in sleeve form.        
A particular type of labelling machine is known wherein each tubular label is formed about a relative cylindrical winding body (commonly called “sleeve drum”) and subsequently transferred onto a relative container, e.g. by introduction of the container inside the tubular label.
This type of labelling machine comprises a carousel rotating about a relative vertical axis to define a substantially circular path portion, along which the labelling machine receives respective successions of unlabelled containers and of rectangular or square labelling material portions from respective input wheels; allows application of sleeve labels onto corresponding containers and releases the labelled containers to an output wheel.
More specifically, the carousel comprises a number of operating units which are equally spaced about the rotation axis, are mounted along the periphery of the carousel and are moved by the latter along the above-mentioned circular path portion.
Each operating unit comprises a bottom supporting assembly adapted to support the bottom wall of a relative container and an upper retainer adapted to cooperate with the top portion of such container to hold it in a vertical position during the rotation of the carousel about the vertical axis.
Each supporting assembly comprises a vertical hollow supporting mount, secured to a horizontal plane of a rotary frame of the carousel, and a cylindrical winding body, engaging the supporting mount in sliding and rotating manner with respect to its axis, and adapted to carry a relative container on its top surface and a relative label on its lateral surface.
Each winding body is movable, e.g. under the control of cam means, between a raised position and a fully retracted position within the relative supporting mount.
In the raised position, each winding body protrudes from a top surface of the relative supporting mount and is adapted to receive a relative label on its lateral surface from the label input wheel; in particular the label is wrapped around the winding body such that the opposite vertical edges of the label overlap one another.
In the fully retracted position, which is reached at the container input and output wheels, the top surface of each winding body is flush with the top surface of the supporting mount so that containers are transferred onto and from the carousel along the same transfer plane.
After the welding of the overlapped edges of a tubular label, the movement of the relative winding body from the raised position to the fully retracted position produces the insertion of the relative container inside the label, making the so obtained container ready to be transferred to the output wheel.
For ensuring proper formation of tubular labels, the labelling web material is cut into rectangular or square portions having a length such that, when wound about respective winding bodies, their leading and trailing ends overlap, thus being weldable to one another with good reliability.
Therefore, in practice, the rectangular or square portions of labelling web material are cut into lengths in slight excess of the perimeter of the winding body, and the overlapping ends are welded, e.g. through localised heat application by means of a sealing bar, at a predetermined distance from the very edge of the radially external end, so that the sealing bar applies heat to an area where the two ends are superimposed.
As a result, the excess amount of labelling web material used for the making of each sleeve label—which ultimately leads to an increased overall cost—remains on the sleeve label surface eventually applied on a respective container as an irregularity, which is generally looked upon as undesirable by food industry companies, particularly for aesthetic reasons.